The field capacity of a soil is 25%, its permanent wilting point is 15% and specific dry unit weight is 1.5 g/cc. If the depth of the root zone of a crop is 80 cm, the storage capacity of the soil is

Concept:

For an irrigation land:

SC = Saturation capacity, FC = Field capacity, OMC = Optimum moisture content, PWP = Permanent welting point and UWP = Ultimate welting point

1. Equivalent depth of water held at field capacity (x) = S × d × Fc

2. Equivalent depth of water held at PWP (x’) = S × d × (PWP)

3. Available moisture/storage capacity of soil (y) = S × d × (Fc - PWP)

4. Readily available moisture content (dw) = S × d × (Fc - OMC)

Given:

Field capacity (F. C) = 25 % = 0.25

Permanent willing point (PWP) = 15 % = 0.15

Depth of the root zone (d) = 80 cm

Dry Unit weight of soil (γ_d) = 1.5 g/cc

Calculations:

The storage capacity \(= \frac{{{\gamma _d} \times d \times \left( {F.C - PWP} \right)}}{{{\gamma _w}}}\)

The storage capacity \(= \frac{{1.5 \times 80 \times \left( {0.25 - 0.15} \right)}}{1} = 12\;cm\)

Hence, the storage capacity of the soil is 12 cm.